NEW YORK (Reuters) – A New York City firefighter recently honored for saving the life of a young boy was killed battling an electrical blaze at a high-rise building that began in a dangerously cluttered apartment, officials said on Sunday.

Gordon Matthew Ambelas, 40, a 14-year veteran of the Fire Department of New York, was among more than 100 firefighters who responded to the fast-moving blaze at the Brooklyn building late on Saturday, officials said.

Ambelas was searching the 19th floor for trapped residents when he was overcome by flames and smoke, New York City Mayor Bill de Blasio said in a late night press conference.

The fire was ruled accidental and started in an air conditioning unit electrical cord pinched between a bed frame and a 19th floor apartment wall, fire officials said on Sunday.

The apartment was heavily cluttered with debris and belongings in what fire officials called “Collyers’ conditions,”named after two brothers who became trapped and died under the rubbish hoarded in their New York apartment in 1947. “These conditions make searches of a fire apartment extremely difficult and dangerous for responding firefighters,” Fire Commissioner Daniel Nigro said in a statement.

Four other people were injured in the blaze, fire officials said.

“We’ve lost a real hero tonight and our hearts are heavy,” de Blasio said. “Unfortunately tonight one of New York’s bravest has paid the ultimate price and we all mourn his loss.”

Ambelas, a married father of two children, was honored in June for helping to save the life of a 7-year-old Brooklyn boy whose head and arm became stuck in a rolling gate, pulling the child 15 feet (4.6 meters) off the ground.

The last New York City firefighter to die in the line of duty was in 2012, according to fire officials.